Facile fabrication of a modified polyamide acid porous membrane for uranium enrichment in wastewater

Abstract

Purification of nuclear wastewater is urgently needed due to the radioactivity and toxicity of uranium. In this work, a novel modified polyamide acid membrane adsorbent (GPAA) was facilely fabricated via a Schiff base reaction between glutaraldehyde and an amino terminated polyamide acid oligomer (NPAA), followed by nonsolvent induced phase separation (NIPS) treatment at room temperature. The resultant GPAA membrane has a hydrophilic surface and a porous structure with a low water contact angle of 29°, and the GPAA membrane exhibited a high surface area of 105 m² g⁻¹ with a multi-scale mesoporous feature. Fast uranium adsorption dynamics of the GPAA membrane were observed with adsorption equilibrium at 16 h at 20 ppm uranium initial concentration. The maximum uranium adsorption capacity was found to be 413 mg g⁻¹ with the chemisorption dominating the uranium enrichment process. Importantly, the resultant GPAA membrane demonstrated an ultrahigh uranium uptake of 350 mg g⁻¹ in acidic aqueous solution (pH = 4), ascribing to the hydrophilic carboxyl and the low isoelectric point membrane surface. Meanwhile, the GPAA membrane manifested excellent acid and salt resistance and good selectivity towards common interfering ions. Furthermore, no apparent structural destruction was observed on the membrane after a three-cycle adsorption–desorption practice. Consequently, the sample preparation techniques and the outstanding adsorption performance made the GPAA membrane an ideal adsorbent candidate for uranium enrichment and separation, especially in acidic wastewater.